In recent years, power transmission systems that contactlessly transmit power from a transmitting device to a receiving device using an electromagnetic induction system or a magnetic field resonance system have become popular. In these power transmission systems, power transmission efficiency is changed depending on the distance or positional relationship between a transmitting coil and a receiving coil. Therefore, in transmitting the power, there is a problem of a decrease in the power transmission efficiency if position gap is caused between the transmitting coil and the receiving coil.